"Garlic does have toxic potential to pets, and is generally more potent than onion, also a member of the Allium species, in causing changes in red blood cells in dogs and cats. This is true in raw, cooked or powdered forms. In theory, "deodorized" garlic is allegedly less toxic, since the disulfides, responsible for both the odor and the toxicity, are usually largely removed.
Garlic is extremely toxic if consumed by dogs.
The veterinarian would be able to advice you whether administering garlic is a preferred option and also how much of it should be administered keeping in mind your pet’s weight, age and breed. Although fleas will leave your dog’s coat if they can taste garlic on the coat, addition of garlic to your pet’s diet will not prevent fleas from falling off the coat.
The article above touts the following benefits of garlic on dogs:
*Lee, K.W., Yamato, O., Tajima, M., Kuraoka, M., Omae, S., Meade,Y. "Hematologic changes associated with the appearance of eccentrocytes after intragastric administration of garlic extracts to dogs."American Journal of Veterinary Research. November 2000. Vol. 61, No. 11, 1446-1450.
Garlic For Dogs: Poison Or Medicine? - Dogs Naturally Magazine
Onions, garlic, chives, and leeks are in the Allium family, and are poisonous to both dogs and cats if the dose is right. Garlic is considered to be about five times as toxic as onions for cats and dogs. Certain breeds and species seem to be more sensitive: Japanese breeds of dogs (e.g., Akita, Shiba Inu) and cats. Onion and garlic poisoning results in oxidative damage to the red blood cells (making the red blood cells more likely to rupture) and gastroenteritis (e.g., nausea, oral irritation, drooling, abdominal pain, vomiting, diarrhea). Other clinical signs of anemia may be seen, and include lethargy, pale gums, an elevated heart rate, an increased respiratory rate, weakness, exercise intolerance, and collapse. Onion and garlic poisoning may have a delayed onset, and clinical signs may not be apparent for several days. While minute amounts of these foods in some pets, especially dogs, may be safe, large ingestions can be very toxic.The safety of enteric-coated garlic products was also studied. Direct administration of pulverized enteric-coated products on the gastric mucosa caused reddening of the mucosa in test animals (dogs). When an enteric-coated tablet was administered orally, it caused loss of epithelial cells at the top of crypts in the ileum in the intestinal tract. Enteric-coated garlic products by pass the stomach and deliver garlic directly into the intestine, which is not a traditional route for garlic intake in any species!